High-frequency ventilation is a type of mechanical ventilation which utilizes a respiratory rate greater than four times the normal value. (>150 (Vf) breaths per minute) and very small tidal volumes. High frequency ventilation is thought to reduce ventilator-associated lung injury (VALI), especially in the context of ARDS and acute lung injury. This is commonly referred to as lung protective ventilation. There are different types of high-frequency ventilation. Each type has its own unique advantages and disadvantages. The types of HFV are characterized by the delivery system and the type of exhalation phase. High-frequency ventilation may be used alone, or in combination with conventional mechanical ventilation. In general, those devices that need conventional mechanical ventilation do not produce the same lung protective effects as those that can operate without tidal breathing. Specifications and capabilities will vary depending on the device manufacturer. Physiology With conventional ventilation where tidal volumes (VT) exceed dead space(VDEAD), gas exchange is largely related to bulk flow of gas to the alveoli. With high-frequency ventilation, the tidal volumes used are smaller than anatomical and equipment dead space and therefore alternative mechanisms of gas exchange occur. Procedure Supraglottic Approach—The supraglottic approach is advantageous as it allows a completely tubeless surgical field. Subglottic Approach Transtracheal Approach High-frequency jet ventilation (passive) In the UK, the Mistral or Monsoon jet ventilator (Acutronic Medical Systems) is most commonly used. In the United States the Bunnell LifePulse jet ventilator is most commonly used. HFJV minimizes movement of the thorax and abdomen and facilitates surgical procedures where even slight motion artifact from spontaneous or intermittent positive pressure ventilation may significantly affect the duration and success of the procedure (for example atrial fibrillation ablation). HFJV does NOT allow: setting specific tidal volume, sampling ETCO2 (and because of this, frequent ABGs are required to measure PaCO2). In HFJV a jet is applied with a set driving pressure, followed by passive exhalation for a very short period before the next jet is delivered, creating "auto-PEEP" (called pause pressure by the jet ventilator). The risk of excessive breath-stacking leading to barotrauma and pneumothorax is low but not zero. In HFJV exhalation is passive (depends on passive lung and chest-wall recoil) whereas in HFOV gas movement is caused by in-and-out movement of the “loudspeaker” oscillator membrane. Thus in HFOV both inspiration and expiration are actively caused by the oscillator, and passive exhalation is not allowed. Bunnell LifePulse jet ventilator High-frequency